The connecting rods had 5/16 inch diameter bolts. Some calculations were done assuming the engine speed was 10,000 rpm. The tensile stresses on the rod bolts were very close to the steel yield strength. The engineers at Carrillo also did some calculations and said the preload needed to be higher and they gave me a recommendation. A bolt stress calculation with that preload said it would work, barely. So, a new set of rods was ordered with larger 3/8 inch diameter bolts. They arrived yesterday. Carrillo and Arias are now part of the same company. They did some calculations on the pistons and they should survive at 10,000 rpm, also.